The present invention is in the field of controlled application of acoustic energy to tissues and cells, and more particularly to assessment and control of acoustic energy as a means of enhancing the permeability of cell and tissue for administration of chemical or biological agents.
Ultrasound-mediated administration of drugs, genes, and other therapeutic compounds into and across cells and tissues has shown significant potential in target drug delivery. For example, studies have shown that appropriately applied ultrasound can reversibly permeabilize viable cells so that exogenous material can enter those cells without killing them. Ultrasound-enhanced delivery to cells has been demonstrated in vitro by uptake of extracellular fluid (Williams, J. Cell Sci. 12: 875-85 (1973)); drugs (Saad and Hahn, Ultrasound Med. Biol. 18: 715-23 (1992)); and DNA into both cells (Fechheimer, et al., Proc. Natl. Acad. Sci. USA 84: 8463-67 (1987); Kim, et al., Human Gene Ther. 7: 1339-46 (1996); Bao, et al., Ultrasound Med. Biol. 23: 953-59 (1997); Wyber, et al., Pharm. Res. 14: 750-56 (1997)) and plant tissues (Zhang, et al., Bio/Technology 2: 996-97 (1991)).
Similarly, acoustic effects of lithotripters have been shown to permeabilize cell membranes. (Holmes, et al., J. Urol. 147: 733-37 (1992); Gambihler, et al., J. Membr. Biol. 141: 267-75 (1994)). Ultrasound also has been shown to increase transport of small drugs and proteins across skin, which is of interest for topical and systemic transdermal drug delivery (Kost and Langer, “Ultrasound-mediated transdermal drug delivery” in Topical Drug Bioavailability, Bioequivalence, and Penetration (Shah & Maibach (eds.)) pp. 91-104 (Plenum Press, New York 1993); Mitragotri, et al., Pharm. Res. 13: 411-20 (1996); (Mitragotri, et al., Science 269: 850-53 (1995); Prausnitz, “Transdermal delivery of proteins: recent advances by modification of skin's barrier properties” in Therapeutic Protein and Peptide Formulation and Delivery (Shahrokh, et al., eds.) pp. 124-53 (American Chemical Society, Washington, D.C. 1997)).
Ultrasound has been a well established diagnostic and therapeutic tool in medicine for decades (Stewart and Stratmeyer, eds., An Overview of Ultrasound. Theory, Measurement, Medical Applications, and Biological Effects (FDA 82-8190) (U.S. Department of Health and Human Services, Rockville, Md. 1983); Suslick, ed., Ultrasound: Its Chemical, Physical, and Biological Effects (VCH, Deerfield Beach, Fla. 1988)). Ultrasonic imaging is widely used at high frequency and low intensity conditions, which are believed to cause no or minimal effects on cells (Barnett, et al., Ultrasound Med. Biol. 20: 205-18 (1994)). Ultrasound also is used therapeutically at somewhat greater intensities to heat tissues for physical therapy and other hyperthermia treatments (Exposure Criteria for Medical Diagnostic Ultrasound: I. Criteria Based on Thermal Mechanisms (NCRP Report No. 113), National Council on Radiation Protection and Measurements (Bethesda, Md. 1992)). Under a very different conditions (that is, a spectrum of lower frequencies and high intensity), routine lithotripsy procedures use focused acoustic energy to noninvasively shatter kidney stones so the fragments can be excreted by the body without surgery (Coleman and Saunders, Ultrasonics 31: 75-89 (1993)). Kidney stone destruction by lithotripsy is believed to be mediated by cavitation. Tachibana, et al., Cancer Lett. 78(1-3): 177-181 (1994); Cancer Lett. 72(3): 195-199 (1993) have reported on the use of topically applied ultrasound in combination with a photosensitizer to kill tumor cells and on the combination of topically applied ultrasound in combination with gas containing microspheres to enhance lysis of thrombi, in Circulation 92(5): 1148-1150 (1995) and U.S. Pat. No. 5,315,998 to Tachibana, et al.
Acoustic cavitation involves the creation and oscillation of gas bubbles in a liquid (Leighton, The Acoustic Bubble (Academic Press, London (1994)). During the low-pressure portion of an ultrasound wave, dissolved gas and vaporized liquid can form gas bubbles. These bubbles then shrink and grow in size, oscillating in response to the subsequent high-and low-pressure portions of the ultrasound wave, a process referred to as stable cavitation. Transient cavitation occurs at greater acoustic pressures, where bubbles violently implode after a few cycles. This implosion can have a number of effects, including transiently raising the local temperature by hundreds of degrees Celsius and the local pressure by hundreds of atmospheres, emitting light by a poorly-understood phenomenon called sonoluminescence, creating short-lived free radicals, and launching a high-velocity liquid microjet. Cavitation also is believed to be responsible for ultrasonic permeabilization of cells and tissues of interest for pharmaceutical applications (Wyber, et al., Pharm. Res. 14: 750-56 (1997); Mitragotri, et al., Pharm. Res. 13: 411-20 (1996); Barnett, et al., Ultrasound Med. Biol. 20: 205-18 (1994)). Nonetheless, the effects of ultrasound parameters on cavitation and cell membrane permeabilization are not sufficiently understood for development and optimization of acoustic techniques in, for example, controlled drug delivery.
It is therefore an object of this invention to provide quantitative assessment and control of acoustic tissue effects.
It is another object of this invention to provide means for enhancing the controlled transportation of molecules into or across cell or tissue barriers.
It is still another object of this invention to provide means for reversibly or irreversibly altering cell or tissue permeability, thereby regulating transport or cell or tissue properties such as viability or structure.